I just finished installing a sony car stereo yesterday and today my hvac blower won't work except for high speed. i realise there is a safety issue where if the fuse is gone the high speed is on another circuit so i checked the fuses but they're all good.
Not sure where to check next.....

 

check your wiring diagram in your chiltons manual (you DO have a repair manual don't you?) look for an in line fuse and check it with an ohm meter. I'm betting you spliced your stereo power into your blower and overloaded the circuit. if you cant find an in line fuse and you ha vent done an actual resistance test on the fuse, change the blower fuse anyway. sometimes fuses can blow up near the base and its hard to see it. If you did wire your stereo to an overloaded circuit its just going to blow again, so figure out exactly what you wired it to.

 

I did some digging and found out the issue was the blower motor resistor. the timing was probably coincidental more than anything. part bought and replaced at $14 and 1/2 hr.